1. Field of the Invention
The present invention relates to a method for producing L-cysteine or related substances. Specifically, the present invention relates to a bacterium suitable for the production of L-cysteine or related substances and a method for producing L-cysteine or related substances utilizing such a bacterium. L-cysteine and L-cysteine-related substances are used in the fields of drugs, cosmetics, and foods.
2. Brief Description of the Related Art
L-cysteine is conventionally obtained by extraction from keratin-containing substances such as hairs, horns, and feathers, or by conversion of DL-2-aminothiazoline-4-carboxylic acid using a microbial enzyme. L-cysteine has also been produced on a large scale by using an immobilized enzyme method and a novel enzyme. Furthermore, it has also been attempted to produce L-cysteine by fermentation utilizing a microorganism.
Microorganisms which are able to produce L-cysteine are known. For example, a coryneform bacterium with increased intracellular serine acetyltransferase activity produces cysteine (Japanese Patent Laid-open (Kokai) No. 2002-233384). L-cysteine-producing ability can also be increased by incorporating serine acetyltransferase which has been mutated to attenuate feedback inhibition by L-cysteine (Japanese Patent Laid-open No. 11-155571, U.S. Patent Published Application No. 20050112731, U.S. Pat. No. 6,218,168).
Furthermore, L-cysteine-producing ability in a microorganism can be enhanced by suppressing the L-cysteine decomposition system. Examples of such microorganisms include coryneform bacteria or Escherichia bacteria in which the activity of cystathionine-β-lyase (U.S. Patent Published Application No. 20050112731), tryptophanase (Japanese Patent Laid-open No. 2003-169668), or O-acetylserine sulfhydrylase B (Japanese Patent Laid-open No. 2005-245311) is attenuated or deleted.
Furthermore, it is known that the ydeD gene which encodes the YdeD protein participates in secretion of the metabolic products of the cysteine pathway (Dabler et al., Mol. Microbiol., 36, 1101-1112 (2000)). Furthermore, techniques of enhancing L-cysteine-producing ability by increasing expression of the mar-locus, emr-locus, acr-locus, cmr-locus, mex-gene, bmr-gene, or qacA-gene, are also known. These loci and/or genes encode proteins which cause secretion of toxic substances from cells (U.S. Pat. No. 5,972,663). emrAB, emrKY, yojIH, acrEF, bcr, and cusA are further examples (Japanese Patent Laid-open No. 2005-287333).
An Escherichia coli has been reported which produces L-cysteine, and which has increased activity of the positive transcriptional control factor of the cysteine regulon encoded by the cysB gene (International Patent Publication WO01/27307).
yhaM is registered at the database EcoCyc (BioCyc Home Page, Summary of Escherichia coli, Strain K-12, version 11.6, E. coli K-12 Gene: yhaM, biocyc.org/ECOLI/NEW-IMAGE?type=GENE&object=G7622) as a gene of unknown function, and it's relation with L-cysteine production is also unknown.